The present disclosure relates to treatments and compounds useful in subterranean formations, and, at least in some embodiments, to treatments and compounds wherein particulates and/or surfaces may be subject to silica scale build-up.
In the production of fluids, such as hydrocarbons or water, from a subterranean formation, the subterranean formation should be sufficiently conductive to permit the flow of desirable fluids to a well bore penetrating the formation. Among others, hydraulic fracturing may be a useful treatment for increasing the conductivity of a subterranean formation. Hydraulic fracturing operations generally may involve pumping a treatment fluid (e.g., a fracturing fluid or a “pad fluid”) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more pathways, or “fractures,” in the subterranean formation. Enhancing a fracture generally involves extending or enlarging a natural or pre-existing fracture in the formation. These fractures generally increase the permeability of that portion of the formation. The treatment fluid may comprise particulates, including proppant particulates that are deposited in the resultant fractures. The particulates are thought to help prevent the fractures from fully closing upon release of the hydraulic pressure, forming conductive channels through which fluid may flow between the formation and the well bore.
It is generally believed that the surfaces of particulates generally comprise minerals, which may react with other substances (e.g., water, minerals, treatment fluids, and the like) that reside in the subterranean formation in chemical reactions caused, at least in part, by conditions created by mechanical stresses on those minerals (e.g., fracturing of the mineral surfaces or the compaction of particulates). These reactions are herein referred to as “stress-activated reactions” or “stress-activated reactivity.” One type of these stress-activated reactions may be diageneous reactions. As used herein, the terms “diageneous reactions,” “diageneous reactivity,” and “diagenesis” include chemical and/or physical processes that, in the presence of water, move a portion of the mineral in a particulate and/or convert a portion of the mineral in a particulate into some other form. A mineral that has been so moved or converted is herein referred to as a “diageneous product” or “diagenic product.” Any particulate comprising a mineral may be susceptible to these diageneous reactions, including natural silicate minerals (e.g., quartz), man-made silicates and glass materials, metal oxide minerals (both natural and man-made), and the like.
Two of the principal mechanisms that diagenesis reactions are thought to involve are “pressure dissolution” and “precipitation processes.” Where two water-wetted mineral surfaces are in contact with each other at a point under strain, the localized mineral solubility near that point may increase, causing the minerals to dissolve. Minerals in solution may diffuse through the water film outside of the region where the mineral surfaces are in contact (e.g., the pore spaces of a particulate pack), where they may precipitate out of solution. The dissolution and precipitation of minerals in the course of these reactions may reduce the conductivity of a particulate pack, inter alia, by clogging the pore spaces in the particulate pack with mineral precipitate and/or collapsing the pore spaces by dissolving solid mineral in the “walls” of those pore spaces. In other instances, minerals on the surface of a particulate may exhibit a tendency to react with substances in the reservoir, formation, and/or treatment fluids that are in contact with the particulates, such as water, gelling agents (e.g., polysaccharides, biopolymers, etc.), and other substances commonly found in these fluids. Molecules from such substances may become anchored to the mineral surface of the particulate. These types of reactivity may further decrease the conductivity of a subterranean formation, inter alia, through the obstruction of conductive fractures in the formation by any molecules that have become anchored to the particulates resident within those fractures. Both types of reactions may generally require the presence of a fluid, such as water, to occur to any significant extent.
Silica (silicon dioxide) appears naturally in a number of crystalline and amorphous forms, all of which are sparingly soluble in water; thus leading to the formation of undesirable deposits. Silicates can be salts derived from silica or the silicic acids, especially orthosilicates and metasilicates, which may combine to form polysilicates. Silica solubility depends on, but not exclusively, a number of factors such as pH, temperature, and ionic composition. Most silicates, except the alkali silicates, are sparingly soluble in water. A number of different forms of silica and silicate salt deposits are possible, and formation of deposits depends, among other factors, on the temperature and pH of the water.